Fumiko Nakazeki

MicroRNA-33b knock-in mice for an intron of sterol regulatory element-binding factor 1 (Srebf1) exhibit reduced HDL-C in vivo

MicroRNAs (miRs) are small non-protein-coding RNAs that bind to specific mRNAs and inhibit translation or promote mRNA degradation. Recent reports, including ours, indicated that miR-33a located within the intron of sterol regulatory element-binding protein (SREBP) 2 controls cholesterol homeostasis and can be a possible therapeutic target for treating atherosclerosis. Primates, but not rodents, express miR-33b from an intron of SREBF1. Therefore, humanized mice, in which a miR-33b transgene is inserted within a Srebf1 intron, are required to address its function in vivo. We successfully established miR-33b knock-in (KI) mice and found that protein levels of known miR-33a target genes, such as ABCA1, ABCG1, and SREBP-1, were reduced compared with those in wild-type mice. As a consequence, macrophages from the miR-33b KI mice had a reduced cholesterol efflux capacity via apoA-I and HDL-C. Moreover, HDL-C levels were reduced by almost 35% even in miR-33b KI hetero mice compared with the control mice. These results indicate that miR-33b may account for lower HDL-C levels in humans than those in mice and that miR-33b is possibly utilized for a feedback mechanism to regulate its host gene SREBF1. Our mice will also aid in elucidating the roles of miR-33a/b in different genetic disease models.

MicroRNA-33 Controls Adaptive Fibrotic Response in the Remodeling Heart by Preserving Lipid Raft Cholesterol

Rationale: Heart failure and atherosclerosis share the underlying mechanisms of chronic inflammation followed by fibrosis. A highly conserved microRNA (miR), miR-33, is considered as a potential therapeutic target for atherosclerosis because it regulates lipid metabolism and inflammation. However, the role of miR-33 in heart failure remains to be elucidated. Objective: To clarify the role of miR-33 involved in heart failure. Methods and Results: We first investigated the expression levels of miR-33a/b in human cardiac tissue samples with dilated cardiomyopathy. Increased expression of miR-33a was associated with improving hemodynamic parameters. To clarify the role of miR-33 in remodeling hearts, we investigated the responses to pressure overload by transverse aortic constriction in miR-33–deficient (knockout [KO]) mice. When mice were subjected to transverse aortic constriction, miR-33 expression levels were significantly upregulated in wild-type left ventricles. There was no difference in hypertrophic responses between wild-type and miR-33KO hearts, whereas cardiac fibrosis was ameliorated in miR-33KO hearts compared with wild-type hearts. Despite the ameliorated cardiac fibrosis, miR-33KO mice showed impaired systolic function after transverse aortic constriction. We also found that cardiac fibroblasts were mainly responsible for miR-33 expression in the heart. Deficiency of miR-33 impaired cardiac fibroblast proliferation, which was considered to be caused by altered lipid raft cholesterol content. Moreover, cardiac fibroblast–specific miR-33–deficient mice also showed decreased cardiac fibrosis induced by transverse aortic constriction as systemic miR-33KO mice. Conclusion: Our results demonstrate that miR-33 is involved in cardiac remodeling, and it preserves lipid raft cholesterol content in fibroblasts and maintains adaptive fibrotic responses in the remodeling heart.

Expression patterns of miRNA-423-5p in the serum and pericardial fluid in patients undergoing cardiac surgery

Background Recently, it has been reported that specific microRNA (miRNA) levels are elevated in serum and can be used as biomarkers in patients with cardiovascular diseases. However, miRNAs expression profiles and their sources in pericardial fluid (PF) are unclear. Methods and Results The purpose of this study was to identify the levels of miRNAs in PF in relation to those in the serum in patients undergoing cardiac surgery. Serum (S) and PF from patients undergoing coronary artery bypass graft (CABG) due to stable angina pectoris (sAP) and unstable AP (uAP) and aortic valve replacement due to aortic stenosis (AS) were analyzed for the detection of miRNAs. We named these samples S-sAP, S-uAP, S-AS, PF-sAP, PF-uAP, and PF-AS, respectively. We first measured the levels of miR-423-5p, which was recognized previously as a biomarker for heart failure. miR-423-5p levels were significantly higher in PF than serum. Although there was no difference in miR-423-5p levels among the PF-AS, PF-sAP, and PF-uAP, its levels were significantly elevated in S-uAP compared with those in S-AS and S-sAP. In order to clarify the source of miR-423-5p in PF, we measured the levels of muscle-enriched miR-133a and vascular-enriched miR-126 and miR-92a in the same samples. miR-133a levels were significantly higher in serum than in PF, and it was elevated in S-uAP compared with S-AS. miR-126 level was significantly increased in serum compared with PF, and the level of miR-92a the similar tendency. miR-423-5p is located in the first intron of NSRP1. There is another miRNA, miR-3184, encoded in the opposite direction in the same region. In vitro experiments indicated that the duplex of miR-423-5p and miR-3184-3p was more resistant to RNase than the duplex of miR-423-5p and miR-133-3p, which may help to stabilize miR-423-5p in the PF. Conclusions Our results suggested that miR-423-5p is enriched in PF, and serum miR-423-5p may be associate with uAP. Its expression pattern was different to that of muscle- and vascular-enriched miRNAs, miR-133a, miR-126, and miR-92a.

Prevention of neointimal formation using miRNA-126-containing nanoparticle-conjugated stents in a rabbit model

Background Despite recent progress with drug-eluting stents, restenosis and thrombosis after endovascular intervention are still major limitations in the treatment of cardiovascular diseases. These problems are possibly caused by inappropriate inhibition of neointimal formation and retardation of re-endothelialization on the surface of the stents. miR-126 has been shown to have the potential to enhance vascular endothelial cell proliferation. Methods and results We designed and constructed a 27-nt double strand RNA (dsRNA) conjugated to cholesterol, which has high membrane permeability, and formed mature miR-126 after transfection. For site-specific induction of miR-126, we utilized poly (DL-lactide-co-glycolide) nanoparticles (NPs). miR-126-dsRNA-containing NPs (miR-126 NPs) significantly reduced the protein expression of a previously identified miR-126 target, SPRED1, in human umbilical vascular endothelial cells (HUVECs), and miR-126 NPs enhanced the proliferation and migration of HUVECs. On the other hand, miR-126 NPs reduced the proliferation and migration of vascular smooth muscle cells, via the suppression of IRS-1. Finally, we developed a stent system that eluted miR-126. This delivery system exhibited significant inhibition of neointimal formation in a rabbit model of restenosis. Conclusions miR-126 NP-conjugated stents significantly inhibited the development of neointimal hyperplasia in rabbits. The present study may indicate the possibility of a novel therapeutic option to prevent restenosis after angioplasty.

Genetic Ablation of MicroRNA-33 Attenuates Inflammation and Abdominal Aortic Aneurysm Formation via Several Anti-Inflammatory Pathways

Objective— Abdominal aortic aneurysm (AAA) is an increasingly prevalent and ultimately fatal disease with no effective pharmacological treatment. Because matrix degradation induced by vascular inflammation is the major pathophysiology of AAA, attenuation of this inflammation may improve its outcome. Previous studies suggested that miR-33 (microRNA-33) inhibition and genetic ablation of miR-33 increased serum high-density lipoprotein cholesterol and attenuated atherosclerosis. Approach and Results— MiR-33a-5p expression in central zone of human AAA was higher than marginal zone. MiR-33 deletion attenuated AAA formation in both mouse models of angiotensin II– and calcium chloride–induced AAA. Reduced macrophage accumulation and monocyte chemotactic protein-1 expression were observed in calcium chloride–induced AAA walls in miR-33−/− mice. In vitro experiments revealed that peritoneal macrophages from miR-33−/− mice showed reduced matrix metalloproteinase 9 expression levels via c-Jun N-terminal kinase inactivation. Primary aortic vascular smooth muscle cells from miR-33−/− mice showed reduced monocyte chemotactic protein-1 expression by p38 mitogen-activated protein kinase attenuation. Both of the inactivation of c-Jun N-terminal kinase and p38 mitogen-activated protein kinase were possibly because of the increase of ATP-binding cassette transporter A1 that is a well-known target of miR-33. Moreover, high-density lipoprotein cholesterol derived from miR-33−/− mice reduced expression of matrix metalloproteinase 9 in macrophages and monocyte chemotactic protein-1 in vascular smooth muscle cells. Bone marrow transplantation experiments indicated that miR-33–deficient bone marrow cells ameliorated AAA formation in wild-type recipients. MiR-33 deficiency in recipient mice was also shown to contribute the inhibition of AAA formation. Conclusions— These data strongly suggest that inhibition of miR-33 will be effective as a novel strategy for treating AAA.

Loss of periostin ameliorates adipose tissue inflammation and fibrosis in vivo

Recent evidence suggests that the accumulation of macrophages as a result of obesity-induced adipose tissue hypoxia is crucial for the regulation of tissue fibrosis, but the molecular mechanisms underlying adipose tissue fibrosis are still unknown. In this study, we revealed that periostin (Postn) is produced at extraordinary levels by adipose tissue after feeding with a high-fat diet (HFD). Postn was secreted at least from macrophages in visceral adipose tissue during the development of obesity, possibly due to hypoxia. Postn−/− mice had lower levels of crown-like structure formation and fibrosis in adipose tissue and were protected from liver steatosis. These mice also showed amelioration in systemic insulin resistance compared with HFD-fed WT littermates. Mice deficient in Postn in their hematopoietic compartment also had lower levels of inflammation in adipose tissue, in parallel with a reduction in ectopic lipid accumulation compared with the controls. Our data indicated that the regulation of Postn in visceral fat could be beneficial for the maintenance of healthy adipose tissue in obesity.